How to Fix an Outlook Express Error 421In Feburary 2016 14,

In Feburary 2016 14,
Open the Microsoft Exchange Server Administrator utility. The access path to the utility will vary depending on the installation procedure used to set up your Exchange Server.
Click the 'Connections' icon in the left-side navigation pane of the Microsoft Exchange Server Administrator window for the server you want to administer. Double-click the Internet Mail Service icon in the right-side pane. This opens the Properties window.
Click the 'Connections' tab in the Properties window, then click the 'Advanced' button. This opens a configuration window.
Set the number for 'Max No. of Inbound Connections' to a high number such as 100. You may need to reset it to higher values until the problem is resolved.
Close all open Exchange Server Administrator program windows to complete the process.
In Feburary 2016 14,